Good Afternoon Todd, 

Thank you for contacting the U of M Extension Service. 

This is not a rhubarb plant. It is a weed. Common burdock. Pull it out. I do not believe the "tree" is part of this weed. If you follow the stems down to the soil, they may be different weeds growing near the birch tree stems. 

You might consider spreading wood chip mulch around the base of the tree, a few inches away from the trunk. The mulch would keep the weeds down, cool the soil and hold the moisture while protecting the roots of the tree. Nice birch tree. 

Here is a link from the U of M Extension Yard and Garden site about tree care: 

https://extension.umn.edu/forestry/tree-selection-and-care

Good Luck!

You are welcome!